The present invention relates to CM-chitin derivatives having a tripeptide, Arg-Gly-Asp (SEQ ID NO: 1), as an essential unit, and salts thereof, as well as a composition for inhibiting adhesion of animal cells and a composition for inhibiting coagulation of blood platelets.
Fibronectin is a protein involved in the cell-extracellular substrate adhesion and is likewise thought to be involved in coagulation of blood platelets and the metastasis of cancer. These interactions are mediated by a series of receptors present in the cell surface region. It is confirmed that these receptors can specifically recognize an amino acid sequence: Arg-Gly-Asp (SEQ ID NO: 1) of the fibronectin although the fibronectin is a macromolecule having a molecular weight of about 250,000 and it has been reported that the sequence plays an important role in the interaction between the receptors and the fibronectin (Nature, 1984, 309, p. 30). Since then, there have been many studies conducted in which an oligopeptide or polypeptide having such an amino acid sequence: Arg-Gly-Asp (SEQ ID NO: 1) is used.
There have been various studies reported, such as a method for inhibiting the coagulation of blood platelets by the use of various linear and cyclic oligopeptides having an Arg-Gly-Asp (SEQ ID NO: 1) sequence (Polymer Preprints, Japan, 1989, 38, p. 3149; Japanese Unexamined Patent Publication (hereinafter referred to as "J. P. KOKAI") No. Hei 2-174797); a method in which a peptide having an Arg-Gly-Asp (SEQ ID NO: 1) sequence is used as a cell movement-inhibiting agent (J. P. KOKAI No. Hei 2-4716); and a method using as a cell-adhesive membrane, a PMMA film on which Arg-Gly-Asp (SEQ ID NO: 1) sequences are immobilized (Polymer Preprints, Japan, 1988, 37, p. 705). In addition, J. P. KOKAI Nos. Hei 1-309682 and Hei 1-305960 disclose a method which comprises peptides having Arg-Gly-Asp (SEQ ID NO: 1) sequences as essential structural units covalently bonded to a polymer and the resulting product is used as a substrate for cultivating animal cells or for biological composite artificial organs and J. P. KOKAI No. Sho 64-6217 discloses a method in which a polypeptide having Arg-Gly-Asp-Ser (SEQ ID NO: 7) sequences is used as a platelet protective agent for blood taken out of the body. Further, there is a known method comprising inhibiting the metastasis of cancer by the use of an oligopeptide having Arg-Gly-Asp (SEQ ID NO: 1) sequences or a polypeptide having the sequence as repeating units (Int. J. Biol. Macromol., 1989, 11, p. 23; ibid, 1989, 11, p. 226; Jpn. J. Cancer Res., 1989, 60, p. 722).
Chitin is a polysaccharide in which N-acetyl-D-glucosamine is linked through the .beta.- (1.fwdarw.4) bond and is a main component of the exoskeleton of Crustacea and Insects. It is widely distributed in lower animals and invertebrates and serves to support and/or protect the organs. The functions thereof correspond to those of cellulose in the plant. Chitin is also called the last biomass, derivatives thereof have been variously studied recently and, in particular, many studies concerning solvent-soluble chitin derivatives have been reported. Among them, CM-chitin in which a carboxymethyl group is bonded to the C-6 hydroxyl group is water-soluble and a very important compound as a starting material for preparing various chitin derivatives. Chitin and derivatives thereof are detailed in "Applications of Chitin Chitosan", edited by the Society for research of chitin chitosan published by Gihodo Publishing Company and "The Last Biomass: Chitin Chitosan", edited by the same Society, published by Gihodo Publishing Company.
The CM-chitin causes deacetylation during carboxylation and this indicates the presence of an amino group in addition to a carboxyl group. The amino group thereof can easily undergo carboxylation with a dibasic acid or a derivative thereof, preferably a polybasic acid anhydride. The N, O-sulfation of the CM-chitin is also easy. However, there is no known compound in which an oligopeptide having an Arg-Gly-Asp (SEQ ID NO: 1) sequence as an essential unit or a polypeptide having the sequences as repeating unit. If such an oligopeptide or a polypeptide is introduced into a compound, it would be expected that the ability of bonding thereof to a receptor and the stability thereof in blood would be greatly enhanced.
Accordingly, an object of the present invention is to provide a novel CM-chitin derivative.
Another object of the present invention is to provide a composition for inhibiting adhesion of animal cells containing the chitin derivative as an effective component.
A further object of the present invention is to provide a composition for suppressing coagulation of blood platelets which comprises the novel CM-chitin derivative as an effective component.
According to an aspect of the present invention, a CM-chitin derivative is provided having, as an essential structural unit, an adhesive peptide represented by the following general formula (I) through any one of an amido bond, an ester bond, an ether bond and a urethane bond on the side chain and salts thereof: EQU -[R.sup.1 ]-[CO]-([X]-Arg-Gly-Asp-[Y]).sub.n -[Z]-[R.sup.2 ]--. . . (I) (SEQ ID NO: 1)
In general formula (I), [ ] means that each corresponding group or residue may be present or absent and if they are present, X and Y each represents an amino acid residue selected from the group consisting of Ser, Gly, Val, Asn and Pro or a peptide residue consisting of two or more of the amino acids; Z represents --O-- or --NH--; one of R.sup.1 and R.sup.2 represents a hydrogen atom, a linear or branched alkyl group having 1 to 9 carbon atoms or an aryl group having 6 to 9 carbon atoms in which the alkyl and aryl groups may be substituted and the other represents a hydrogen atom, a linear or branched alkylene group having 1 to 9 carbon atoms or an arylene group having 6 to 9 carbon atoms wherein the alkylene and arylene groups may be substituted; and n is an integer ranging from 1 to 5.
Examples of substituents for R.sup.1 and R.sup.2 include halogen atoms, carbonyl, carboxyl, amino, hydroxyl, sulfo, aryl, nitro and cyano groups, unsaturated hydrocarbon group which has a double bond and triple bond and they may have two or more substituents.
According to another aspect of the present invention, there is provided a composition for inhibiting adhesion of animal cells or for suppressing coagulation of blood platelets comprising the foregoing CM-chitin derivative as an effective component.